The plastic films sold in the market for keeping food fresh are shown packaged as in FIG. 1A, wherein outside of the packing box 100, there is provided a strip of cutting teeth 101. In order to use the plastic film, people have to find the starting end of the roll of plastic film, pull the film outwardly to a predetermined proper length, cause the film to contact the cutting teeth 101, and then by using the cutting teeth, tear the film gradually. During such operation, if the people do not tear the film carefully, the plastic films are always torn in an irregular manner or they tend to stick together because of static electricity. This makes people very unpleasant and feel very frustrated, and besides, it is a waste of materials. Furthermore, it is very easy for people to injure their hands due to carelessness. In order to avoid the defects mentioned above, there is also provided or known a box having a sliding cutter for the plastic film, as shown in FIG. 1B. In order to use the plastic film, the roll of plastic film is firstly put into the storage box, however, after a long period of use, the inner space of the storage box will become very dirty and will stain the plastic film which was clean originally. Moreover, as shown in FIG. 2A, the cutting blade 202 upon the push button 201 of the cutting means disposed within the storage box is formed with one cutting edge at one side, such that the plastic film can only be cut in one direction. After one cutting operation is completed, the push button 201 has to be pushed back to its original position. Furthermore, as shown in FIG. 2B, the one-sided cutting blade 202 is inserted into the push button 201 with its cutting edge inclined inwardly so as to cut the plastic film. A resisting force tending to obstruct the cutting of the plastic film will therefore naturally be developed whereby the cutting end of the plastic film will be pushed downwardly and will tend to be gathered within the vicinity of the button by means of the cutting edge of the cutting blade 202. As a result, the plastic film has to be pulled tightly against the T-shaped furrow of the cutter. If the pulling force is not sufficient, the plastic film will be gathered as described before and cannot be properly cut.
Moreover, the size of the plastic film storage box with the sliding cutter as shown in FIG. 2A is fixed and not suited for plastic films with different sizes. This is also a defect of the improved plastic film storage box provided with a sliding cutter.